This Demonstration simulates the response of photosynthesis  (  ) to photosynthetic photon flux density PPFD (  ). The equations are based on the leaf model of photosynthesis [1] that predicts  based on the most limiting of three processes: (1) the kinetics of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (or rubisco) for fixing  , (2) the rate of RuBP regeneration associated with electron transport rates on the thylakoid membrane (RuBP), and (3) the rate in which inorganic phosphate, required for regenerating ATP from ADP, is released during the utilization of triose phosphate (TPU). While the functions associated with all three of these limiting processes are shown (Rubisco, RuBP, and TPU), the actual modeled rate of photosynthesis will be the lowest of the three processes. The modeled rates of photosynthesis are indicated by the net photosynthesis curve  (solid black line). Vary any of the parameters and/or environmental conditions to see the impact on the modeled photosynthesis over the range of PPFD. The equations from the original model [1] have been corrected with the temperature functions from [3] for rubisco-limited photosynthesis, [2, 4, 6] for RuBP-limited photosynthesis, and [5] for TPU-limited photosynthesis. Changes in the environmental conditions introduce changes in the leaf intercellular  concentration  , which are not simulated here.
The leaf's environmental conditions include leaf intercellular  concentration  (  ), oxygen concentration  (  ), and leaf temperature  (°C). The photosynthetic parameters include the maximum rate of carboxylation  (  ), maximum rate of electron transport through photosystem II  (  ), rate of triose phosphate utilization  (  ), and rate of mitochondrial respiration  (  ). The temperature dependence of  is derived using the data from [2] but with the temperature response of [6] modified as in [4] to normalize values to 25°C. Under the heading "RuBP-Limited  Adjustments", you can vary the temperature optimum  and the temperature at which  falls to  of its value at  (  ). The default parameterization for these values are from [2] for tobacco grown at 25 °C, but values for a range of species are provided elsewhere [6]. Changes in  and  only affect  when  . You can also vary the leaf absorbance  (unitless), the ratio of photosystem II to photosystem I  (unitless), the curvature of the PPFD response curve  (unitless), and the quantum efficiency of PSII ΦPSII (unitless). [1] G. D. Farquhar, S. von Caemmerer, and J. A. Berry, "A Biochemical Model of Photosynthetic  Assimilation in Leaves of  Species," Planta, 149(1), 1980 pp. 78–90. doi: 10.1007/BF00386231. [2] C. J. Bernacchi, C. Pimentel, and S. P. Long, " In Vivo Temperature Response Functions of Parameters Required to Model RuBP-Limited Photosynthesis," Plant, Cell & Environment, 26(9), 2003 pp. 1419–1430. doi: 10.1046/j.0016-8025.2003.01050.x. [3] C. J. Bernacchi, E. L. Singsaas, C. Pimentel, A. R. Portis Jr, and S. P. Long, "Improved Temperature Response Functions for Models of Rubisco-Limited Photosynthesis," Plant, Cell & Environment, 24(2), 2001 pp. 253–259. doi: 10.1111/j.1365-3040.2001.00668.x. [4] C. J. Bernacchi, C. J. Bagley, S. P. Serbin, U. M. Ruiz-Vera, D. M. Rosenthal, and A. VanLoocke, "Modeling C3 Photosynthesis from the Chloroplast to the Ecosystem." Plant, Cell & Environment, 2013, forthcoming. [5] P. C. Harley, R. B. Thomas, J. F. Reynolds, and B. R. Strain, "Modelling Photosynthesis of Cotton Grown in Elevated  ," Plant, Cell & Environment, 15(3), 1992 pp. 271–282. doi: 10.1111/j.1365-3040.1992.tb00974.x. [6] T. June, J. R. Evans, and G. D. Farquhar, "A Simple New Equation for the Reversible Temperature Dependence of Photosynthetic Electron Transport: A Study on Soybean Leaf," Functional Plant Biology 31(3), 2004 pp. 275–283. doi: 10.1071/FP03250.
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